This invention relates to drilling tools for hollow-stem augers, and particularly to an auger cutter head for drilling a hole sized to receive the hollow-stem auger therein in hard ground formations. More particularly, this invention relates to an auger cutter head having a body and plurality of chisel bits and cutter blades oriented and arranged about the circumference of the body to improve drilling performance of the cutter head and extend the useful life of the cutter head.
A hollow-stem auger is recognized in various construction, geotechnical, and environmental fields as a versatile, fast, and effective tool for simultaneously advancing and casing a drill hole in a wide variety of ground formations. Typically, a center stem of the auger is quickly removed once the desired drilling depth is achieved to allow working inside the auger using coring tools, soil sampling equipment, in-hole hammers, back rods and cables, environmental monitoring equipment, and other apparatus. The hollow-stem auger is widely used in conjunction with ground water monitoring and hazardous waste operations and other geotechnical and exploration drilling applications.
It is well known to mount a cutter head on the bottom end of a hollow-stem auger to provide means on the auger for penetrating and drilling into wet, dry, soft, hard, loose, or coarse ground formations as the hollow-stem auger is driven into the ground using a conventional drill rig. The cutter head rotates and advances with the auger as the auger is driven into the ground by the drill rig. Conventional cutter heads include chisel bits and cutter blades that cooperate to break up the ground and any foreign objects therein, thereby generating ground waste materials known as "spoils" or "cuttings." The conventional auger itself trails the cutter head and typically includes a central shaft and a series of slightly tapered concave flights. These flights are mounted on the central shaft of the auger and are designed to throw these cuttings against the central shaft so that the cuttings can be carried upwardly toward the surface by the flights as the auger and cutter head are rotated and driven further into the ground by the drill rig.
It has been observed during the development of this invention that the various components (e.g., flight sections, bit blocks, and chisel bits) included in conventional cutter heads wear out quickly as a result of repeated contact with a variety of difficult-to-cut hard objects in the ground. In many environmental applications, it is necessary to drive an auger cutter head into ground in an environmental clean-up area that contains, for example, railroad ties, cement reinforcing rods, discarded appliances, and other items that are difficult to cut using a conventional auger cutter head. In geotechnical and exploration applications, it is often necessary to drill into hard-to-drill formations, including gravels, hardpan, till, and caliche.
One problem with conventional cutter heads is that they include flighting sections and bit blocks that form the radially outermost part of the cutter head and function as the primary means for engaging the ground formation to ream or gauge the hole being drilled. These conventional flighting sections and bit blocks take a beating as a result of being banged against hard ground formations and hard objects in the ground during rotation of the advancing cutter head. These conventional cutter head components tend to wear out quickly if the cutter head is used to drill a hole in hard ground formations littered with buried hard objects or filled with difficult-to-drill formations. These conventional cutter heads have a tendency to drag or become wedged in the hole because the cutter head is not effectively reaming or gauging the hole by cutting sufficient clearance for the body of the cutter head to go further downward into the ground. Also, it has been observed that the torque and shock loading on the auger cutter head increased as the conventional cutter head struggled to penetrate and cut through hard ground formations and/or various hard objects littered through the strata in ground that had been used as a refuse dump. A new cutter head configured to reduce exposure of flighting sections, bit blocks, and other adjacent components to contact with hard objects and ground formations and enhance the means for reaming or gauging the hole being drilled would be an improvement over conventional cutter heads.
Another problem with conventional cutter heads is that they include rotatable chisel bits that wear unevenly as the chisel bits rotate about an axis of rotation in the bit blocks as they frictionally engage ground and other material during drilling of the hole. It has been observed that many conventionally mounted and oriented chisel bits tend to flatten or wear on one side because they are not rotating properly about their axis of rotation during rotation of the conventional cutter head about its own axis of rotation. A new cutter head configured to orient the chisel bits so as to produce consistent rotation of each bit during drilling of the hole would be an improvement over conventional cutter heads.
A more durable auger cutter head would better meet the demands encountered, for example, during environment clean-up drilling or geotechnical exploration drilling. An object of the present invention is to provide an improved cutter head having flighting sections, bit blocks, chisel bits, and other components that are mounted, arranged, and oriented in such a way as to enhance the drilling performance and extend the useful life of the auger cutter head.
According to the present invention, an improved cutter head is provided for use with a hollow-stem auger or the like. The cutter head rotates with the hollow-stem auger about its axis of rotation to drill into the ground and produce a hole having a cylindrical side wall of a predetermined inner diameter. The cutter head includes a cutter body having means for connecting to the hollow-stem auger to rotate and move therewith and a plurality of spaced-apart cutting assemblies mounted on the cutter body.
A first of the cutting assemblies includes a first outside chisel bit having a base and a tip, and first mounting means for mounting the base on the cutter body to position the tip at a first predetermined distance from the axis of rotation of the hollow-stem auger to provide means for gauging the predetermined inner diameter of the hole. The first outside chisel bit penetrates material in the ground to be cut and the tip generates the cylindrical side wall of the hole to be drilled in response to motion of the cutter body around and along the axis of rotation of the hollow-stem auger during drilling of the hole.
In preferred embodiments, the first mounting means includes a flighting section mounted on the cutter body and a bit block fixed to the flighting section to support the first outside chisel bit for rotation about its own axis of rotation upon frictional engagement with the ground during drilling of the hole. Advantageously, the flighting section and the bit block of this first cutting assembly (and of every other cutting assembly on the cutter head) are offset from the tip of the first outside chisel bit in a radially inward direction toward the axis of rotation of the hollow-stem auger so that none of these flighting sections and bit blocks ream or gauge the predetermined inner diameter of the hole as it is being drilled, thereby reducing wear of these parts. Instead, the improved cutter head is constructed so that only the tip of the first outside chisel bit reams or gauges the predetermined inner diameter of the hole as the tip orbits about the axis of rotation of the hollow-stem auger during drilling of the hole.
Also in preferred embodiments, a second outside chisel bit is added so that two of the chisel bits on the cutter head are positioned to ream or gauge the hole being drilled. These two outside chisel bits are spaced apart from one another to balance the cutter head and center the cutter body as it is driven downwardly further into the ground during drilling of the hole. It has been observed that many conventional cutter heads actually produce unwanted elliptically shaped drilled holes because they are unable to remain in a proper, centered position within the hole being drilled.
In addition, a third chisel bit (known as an "inside" chisel bit) is mounted and oriented to enlarge a pilot hole dug by a conventional pilot bit along the axis of rotation of the hollow-stem auger to provide a large diameter "coring hole" inside the hollow-stem auger into which various coring, sampling, and monitoring equipment can be inserted once the hole drilled by the cutter head has been completed. Further, a fourth chisel bit (known as a "center" chisel bit) is mounted and oriented to penetrate and fracture material in the ground between the inside and the two outside chisel bits.
Preferably, each of the four chisel bits in the illustrated embodiment is mounted and oriented to align its axis of rotation at a predetermined compound angle relative to the axis of rotation of the cutter body (which is coextensive with the axis of rotation of the hollow-stem auger). These compound angles have been preselected to maximize consistent rotation of each chisel bit about its own axis of rotation upon frictional engagement with the ground during drilling of the hole. Advantageously, such rotation distributes the load on the shoulder of each chisel bit and promotes more even wear on the rotatable chisel bits to enhance drilling performance and extend the useful life of the chisel bits.
A cutter head in accordance with the present invention is configured to cut harder formations at increased penetration rates over a longer useful life. Thus, such improved cutter head of the present invention is designed to reduce drilling costs and improve drilling performance.
It is contemplated that a cutter head in accordance with the present invention can be produced to include, for example, three chisel bits. When drilling smaller diameter holes, it is convenient to provide a cutter head including only an outside chisel bit, an inside chisel bit, and a center chisel bit. Depending upon the application, it is within the scope of the present invention to use an outside chisel bit on a cutter head in combination with one or more other chisel bits.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of a preferred embodiment exemplifying the best mode of carrying out the invention as presently perceived.